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Abstract

A simple and efficient technique for large-area manufacturing of concave microlens arrays (MLAs) on silica glasses with femtosecond (fs)-laser-enhanced chemical wet etching is demonstrated. By means of fs laser in situ irradiations followed by the hydrofluoric acid etching process, large area close-packed rectangular and hexagonal concave MLAs with diameters less than a hundred of micrometers are fabricated within a few hours. The fabricated MLAs exhibit excellent surface quality and uniformity. In contrast to the classic thermal reflow process, the presented technique is a maskless process and allows the flexible control of the size, shape and the packing pattern of the MLAs by adjusting the parameters such as the pulse energy, the number of shots and etching time.

Figures (9)

Schematic of the fabrication process. First, the laser pulses are focused by an objective lens, inducing crater arrays on the sample surface. Then, the sample is treated by ultrasonic-assisted HF etching. Finally, the sample is cleaned by the ultrasonic bath in acetone, alcohol and deionized water, respectively. The inset presents the 3D profile of the rectangular microlens array.

Morphology revolution of the samples at different stage of the fabrication process. For (a)-(c) the rectangular microlens array, the chemical etching time, t, is 0, 45 and 90 min, respectively. The hexagonal-packed microlens array are present in (d)-(f), and t = 0, 25 and 45 min, respectively. The images are captured by an optical microscope with tungsten light source.

The results of 3D measurements of the MLAs. (a) and (b), the cross-section and the 3D profiles of the rectangular microlens array. The aperture diameter, D, and the sag height, h, of the microlens array are about 67.05 μm and 10.28 μm, respectively. (c) and (d), the 3D and cross-section profiles of the hexagonal-packed microlens array. D = 30.54 μm, h = 3.35 μm.

Relationship between the processing parameters and the profile of microlenses. (a) and (b) show the energy dependency of aperture diameter, D, and sag height, h, respectively; (c) and (d) are the influence of the number of shots, N, on D, and h, respectively; (e) and (f) show the influence of E and N on the curvature radius of the microlens, respectively.